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A Natural Selection

By Olivia Judson July 22, 2008 7:44 pmJuly 22, 2008 7:44 pm

(The fourth part in a series celebrating Charles Darwin.)

Last week, I discussed how evolutionary biology has changed since 1859, the year Darwin first published “On the Origin of Species.” But the subject of evolution isn’t the only thing that’s changed since then. There’s been plenty of actual evolution, too. For although we tend to think of evolutionary change as being something that only takes place over the course of millions of years, it isn’t. It’s going on here, now, all around us. So, this week, I thought I’d round up some examples of recent evolutionary change in nature. (What do I mean by recent? Within the last 40 years.)

I’m not intending to be comprehensive — that would take a book or two. Instead, I want to sketch a few examples of natural selection that have caught my fancy, and through them consider different aspects of evolutionary change, and what it takes to show it.

Galápagos finches. No discussion of evolution in nature would be complete without mention of the evolution of beak size in finches in the Galápagos archipelago.

Every year since 1973, large numbers of medium ground finches (Geospiza fortis) living on the island of Daphne Major have been marked, weighed and measured, and so have their chicks. In these finches, survival largely depends on the ability to open seeds; this depends on beak size. Bigger beaks allow the opening of larger seeds. How many seeds there are depends on the weather; some years seeds of all sizes are abundant, and the finches thrive. In other years, most seeds are scarce, and many birds die. Large-scale death affects the genetic make-up of the population, because both beak size and body size has a large genetic component. If all the birds with smaller than average beaks die in a given year, they take their genes with them.

Over the course of 30 years, annual measurement of finches shows that both body size and beak size evolved significantly. But they didn’t do so in a smooth, consistent fashion. Instead, natural selection jittered about, often changing direction from one season to the next.

As the abundance of different seeds fluctuated, so too did the beak sizes. One year, larger beaks were more successful; then it was smaller beaks. Over time, the average shape of the beak kept shifting, but it did so in an unpredictable, erratic sort of way, like a drunk man staggering about. Thus, some of the most dramatic changes were later reversed, and if beaks had only been measured at the beginning and at the end of the thirty years, the total amount of evolutionary change would have been underestimated. (Beak size has continued to evolve: the arrival on the island of a competitor for large seeds has subsequently favored small beak sizes in Geospiza fortis. Many individuals with larger beaks starved to death.)

Field mustard. Between 2000 and 2004, southern California had a severe drought. For many plants, including field mustard (a scrawny annual plant with little yellow flowers), a drought means a shorter growing season. A shorter growing season means that plants that flower earlier are more likely to leave seeds than plants that flower later — which are in danger of dying before they’ve finished reproducing. Since flowering time has a large genetic component, a drought — by favoring plants that flower earlier — could cause an evolutionary shift towards early flowering.

Has it?

Yes. The beauty of plants is that they make seeds — small packets of genes that can be stored for a period. This means that the genes of the past can, in principle, be compared directly with the genes of today. And an experiment in which field mustard plants grown from seeds collected in 1997 and in 2004 were planted together, under controlled conditions, showed clear differences in flowering times: the plants from 2004 flowered significantly earlier.

Moreover, in both years, seeds were collected from two sites, one where the soil is sandy and doesn’t hold water well, and the other where the soil stays wet for longer. As you’d expect, plants from the dry site showed a more dramatic shift than plants from the wet site. In the course of just 7 years, then, natural selection caused the plants to evolve an earlier flowering time.

Croatian lizards. In 1971, five pairs of adult wall lizards (Podarcis sicula) were brought to the tiny Croatian island of Pod Mrčaru from the nearby island of Pod Kopište. These five pairs have since given rise to a thriving lizard population — and one that has developed some interesting differences from the lizards that live on Kopište.

Lizards on Mrčaru now have larger heads and stronger bites than those living on Kopište, and they eat far more in the way of leaves and other plant material. Whereas the diet of native Kopište lizards is only about 7 percent plant matter, Mrčaru lizards are much more prone to a vegetarian habit. In spring, their diet is about 34 percent from plants; in summer that almost doubles, to 61 percent.

Plants are hard for animals to digest, and most plant-eaters rely on micro-organisms to help them. They also, typically, have complicated stomachs — think of the fermentation chambers in a cow, or the enlarged crop of that strange leaf-eating bird, the hoatzin. Intriguingly, the Mrčaru lizards appear to have evolved something similar. Their stomachs now have cecal valves, which divide the stomach into compartments, allowing for slower digestion and fermentation. Cecal valves are rare among lizards and snakes: fewer than 1 percent of species have them. At the same time, the Mrčaru lizards have acquired some novel micro-organisms in their guts (but whether these are helping break down plant fibers, or are some sort of sinister parasite, remains to be seen).

This study is one of the most intriguing I’ve come across. It suggests that arrival in a new environment can result in dramatic changes to an organism within fewer than 40 lifetimes. But so far, the basis of these various changes remains unknown: there’s an outside possibility that they are induced by leaf eating, and are thus due to the environment rather than genetics. (This seems unlikely — even lizards that are just hatched, and haven’t had a chance to do much eating, have the valves. But without doing the genetics, we can’t be sure; until that has been looked at, the changes cannot definitely be attributed to natural selection.) For now, natural selection for efficient plant-eating is the main suspect for this whole suite of changes, but the case is not yet closed.

Other examples. I don’t have space to go into other examples in detail, but to give a sense of what else is out there, here’s a partial list.

The fruit fly Drosophila subobscura has been evolving bigger wings in higher latitudes in North and South America; mosquitoes that live in pitcher plants hunker down for the winter later in the year than they used to; in a forest in southern England, great tits have been shrinking (great tits are songbirds).

Double the time frame to the past 80 years, and I’d have to add many more; of these, my favorite is the decline in head size of Australian frog-eating snakes in response to the arrival of poisonous toads in 1935 (a smaller head makes it harder to eat a deadly toad). And I haven’t even begun to mention the countless examples of pests that have evolved resistance to pesticides and bacteria that have evolved resistance to antibiotics, nor the thousands of laboratory experiments showing evolution in the simple environments of test tubes and petri dishes. Also omitted: several examples of new species that are in the process of forming (I want to look at these in a future column).

In short, evolution never takes a vacation: it’s going on all the time.

Yet we tend not to notice it. Why? The finches can help us here. That study tells us two things. First, from one year to the next, even the most dramatic changes are, to our eyes, small — which is to say, you have to measure them to detect them. The reason is that although birds differ from one another in their abilities to handle the various seeds, the differences are subtle. It’s not as if one bird has a beak 100 times mightier than another’s. When you add to this the tendency of natural selection to jerk around, it’s no surprise that we often don’t notice evolution as it happens. It also sheds light on why changes in the fossil record often appear to be slow: these studies show that change can be continual without really getting far from the starting point. Second, getting data as good as that is hard work. Most datasets are not so complete or robust.

At least one other lesson can be drawn from all these studies. Natural selection has its most dramatic effects when an organism’s environment is perturbed in some sustained way — prolonged droughts, the arrival of species that compete for food, warmer winters, the use of pesticides. If we humans continue to increase our impact on the globe, we’re likely to see lots more evolution. And soon.

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NOTES:

For beak size in Galápagos finches, see Grant, P. R. and Grant, B. R. 2002. “Unpredictable evolution in a 30-year study of Darwin’s finches.” Science 296: 707-711 and Grant, P. R. and Grant, B. R. 2006. “Evolution of character displacement in Darwin’s finches.” Science 313: 224-226. For evolution of flowering time in field mustard, and for its genetic basis, see Franks, S. J., Sim, S. and Weis, A. E. 2007. “Rapid evolution of flowering time by an annual plant in response to a climate fluctuation.” Proceedings of the National Academy of Sciences USA 104: 1278-1282. For the evolution of cecal valves in Croatian lizards, see Herrel, A. et al 2008. “Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource.” Proceedings of the National Academy of Sciences USA 105: 4792-4795.

For wing size in fruit flies, see Huey, R. B. et al 2000. “Rapid evolution of a geographic cline in size in an introduced fly.” Science 287: 308-309 and Gilchrist, G. W. et al 2004. “A time series of evolution in action: a latitudinal cline in wing size in South American Drosophila subobscura.” Evolution 58: 768-780. For hunkering down time in mosquitoes, see Bradshaw, W. E. and Holzapfel, C. M. 2001. “Genetic shift in photoperiodic response correlated with global warming.” Proceedings of the National Academy of Sciences USA 98: 14509-14511. For body size in great tits, see Garant, D. et al 2005. “Evolution driven by differential dispersal within a wild bird population.” Nature 433: 60-65. For head size in Australian snakes, see Phillips, B. L. and Shine, R. 2004. “Adapting to an invasive species: toxic cane toads induce morphological change in Australian snakes.” Proceedings of the National Academy of Sciences USA 101: 17150-17155.

Many thanks to Dan Haydon, Gideon Lichfield and Jonathan Swire for insights, comments and suggestions.

Oh man, I am dying for the article about the evolution of new species.

One thing that I”m happy this article touched on is the idea that the environment itself changes rather erratically. We usually think of evolution as working toward some large goal, of pulling one species or another in one direction. The example with the finches shows clearly that since the environment conditions themselves may slide, convulse, and even cycle, natural selection itself may do nothing more than pull an animal around by its nose for a few decades. But it’s still working!

One problem with all these wonderful examples is that the Creationists will cheerfully acknowledge that “micro” evolution is possible. But they will point gleefully to the lack of a definite speciation event. Of course, there may have been a sequence of changes that could be termed a speciation event in that it may have discouraged mating between changed and unchanged (or differently changed) individuals — creating, in effect, a new species. And, given more time, we’re all certain that this will happen again and again — as it has since life began. But, the Creationists will say, you haven’t shown it to have happened, so we don’t believe it can.

We can only hope that some unambiguous such change will happen soon. But it still won’t convince the doubters.

Dr. Judson’s examples imply that recent evolution is only by natural selection. “Different aspects of evolutionary change” are not considered. The “just so” stories are fine, but adaptive evolution also occurs through chance variation in small isolates (“random drift”) and, as pointed out in commentary #2, adaptive evolution is linear whereas speciation may involve branching into two lines, sometimes without any visible adaptation. Yes, “evolution never takes a vacation” but what’s “going on all the time” is more than just natural selection.

Are the big-beaked finches a different variety of Geospiza fortis and the small-beaked finches yet another?

As mustard plants, lizards, and snakes evolve different characteristics from their ancestors are they varieties moving toward speciation? Is this the way species are formed: first as varieties of an ancestral species and later as separate species?

Are there different living varieties of homo sapiens, each having different characteristics from the other? Could these varying characteristics happen in our intellectual powers, or in our behavior toward each other? Are good and evil human beings products of natural selection?

What are the rules for determining if the offspring of species constitute new varieties of that species?

In “The Origin of Species by Means of Natural Selection,” Chapter II, Mr. Darwin wrote:

“Hence in determining whether a [life] form should be ranked as a species or a variety, the opinion of naturalists having sound judgment and wide experience seems to be the only guide to follow. … That varieties of this doubtful nature are far from uncommon cannot be disputed.”

In her book, “The Sociopath Next Door,” psychologist and author Martha Stout describes in the course of more than two hundred pages the characteristics and dangers of sociopaths. She writes on page 9:

“About one in twenty-five individuals are sociopathic, meaning, essentially, that they do not have a conscience. It is not that this group fails to grasp the difference between good and bad; it is that the distinction fails to limit their behavior. The intellectual difference between right and wrong does not bring on the emotional sirens and flashing blue lights, or the fear of God, that it does for the rest of us. Without the slightest blip of guilt or remorse, one in twenty-five people can do anything at all.”

Ms. Stout is concerned about how to classify sociopaths. On page page 13 she writes:

“Singular in its ability to unnerve even seasoned professionals, the concept of sociopathy comes perilously close to our notions of the soul, of evil versus good, and this association makes the topic difficult to think about clearly. And the unavoidable them-versus-us nature of the problem raises scientific, moral, and political issues that boggle the mind. How does one scientifically study a phenomenon that appears to be, in part, a moral one? Who should receive our professional help and support, the “patients” or the people who must endure them? Since psychological research is generating ways to “diagnose” sociopathy, whom should we test? Should anyone be tested for such a thing in a free society? And if someone has been clearly identified as a sociopath, what, if anything, can society do with that information? No other diagnosis raises such politically and professionally incorrect questions, and sociopathy, with its known relationship to behaviors ranging from spouse battering and rape to serial murder and warmongering, is in some sense the last and most frightening psychological frontier.”

If Ms. Stout is correct about the nature of 4% of our population, then Texas, where I live and which has a population of about 23.5 millions people, is home to 940,000 sociopaths, many of them armed. Do these citizens represent a variety of homo sapiens?

My compliments to Ms. Judson and the Times for up-to-the-minute reporting on the evolutionary process. What could demand more patience, or informed research, from a journalist? Given the rapid pace of climate change, we will certainly want to watch such things as the changes in range of tree species. And I hope we will hear more of such surprises as the sudden compartmentalization of lizard stomachs as reported here. Is it worth speculating on whether such a development may have had its roots in a latent genetic capability?

Once again Olivia Judson gives us hard facts and specifics in the face of ideology based right were this type of argument is not part of their game. I did like the examples and how she illustrated the mechanism.
I tend to think the best you can do is continue to show specific examples on you side and eventually you win out.
I like the idea that good science never ceases to show itself and bad science and bad ideas become increasingly in bread and cut out from reality over time.
Great article on evolution process occurring as we watch and well written.

I liked the way the article mentioned examples of evolution backtracking, zigzagging, and so forth. Evolution is not following a “master plan,” and it’s not intelligent. So, for example, it often takes an inelegant approach to problem-solving, such as making a snake’s head too small to swallow a poisonous toad, rather than making the snake immune to the toad toxin, and so forth!

The evolutionary adaption that recently caught my eye was the popping up of a variety of the coca plant, the Boliviana Negra, which is resistant to glyphosate (also known as RoundUp), and which can be found here: //www.wired.com/wired/archive/12.11/columbia.html .

Chris: Maybe not the real speciation that will convince Creationists, because it happened in an artificial environment, but still quite interesting is this //myxo.css.msu.edu/lenski/pdf/2008,%20PNAS,%20Blount%20et%20al.pdf , where a new kind of E.coli, able to digest citrate, was created by random evolution. Given the fact, that one of the characteristics of E.coli that makes it different from similar strains of bacteria is the fact, that E.coli does NOT digest citrate, we have here the evolution of a new species: E.coli, digesting citrate!

If one is interested in beak sizes and evolution a wonderful book – The Beak of the finch’ is the one I would recommend. It is written by a scientist couple who spent time on Galapagos. The book reads like a story book than a scientific thesis.

Obviously the writer is ignorant about genetics as a change in morphology is not necessary a sign of evolution. In most of the cases in the above scenarios a minor genetic change of one allele for another may account for the difference. To honestly claim evolution you would at least most likely have to prove that a gene has a change in actual effect such as from determining eye color to determining eye shape. I see no evidence that any of these examples does that. These examples are so poorly researched that I am not sure that in some cases the observed changes are even genetically based. I do know thought that “natural” selection can determine the rate of occurrence of certain traits within a population. That too has not been considered in these examples.

Of course evolution is not confined to god’s dumb creatures. Her facsimile in humanity is constantly evolving and I guess that the next major evolution will be of a collective nature. Perhaps the adoption of a Collective Conscience will be an adaption appropriate for the survival of the species and as it happens for life on this particular rock.

Of course this will require a level of self sacrifice and biological symbiosis, we with our peers and of course the dumb creatures.

This particular adaption that I foresee of course presumes that the direction of both evolution and creative design is towards a heightened Consciousness.

The current paradigm social neo-Darwinism suggests the creator is a rapacious and wrathful deity.

With all due respects to a hot shot of evolutionary vulgarisation, when Darwin (or anyone serious) talked about evolution it wasn’t about the thousands of little blips thet occur to result in a permanent progression or degression of a species. What you’re is what you’re describing are the blips. How about providing a concrete definition of YOUR kind of evolution and one defining the difference between change and progress/regress so the public can understand the differences. Were you to look at a tiny sample of humans and note the differences in 2 or 3 generations you could concoct a theory about why one jaw was different or one group had more recessive eyes than another. Although, I guess that you are proof that in less than 40 years, the definitions of “evolution” and “science” can change.

Great article. I am an avid organic garden supporter and am extremely concerned at the possibilities of evolution due to GMO’s. Just the monoculture alone would seem to destroy future food possibilities that could evolve to survive in a variety of climate situations, which seem to be what is in store for the planet. Would love to hear your comments on this.

Your article posits what I believe to be a fundamental rule of evolution : Changes occur in ALL directions, at ALL speeds, in VARYING ways, ALL THE TIME.

Though close observation and measurement, as you wrote, is required to produce any sort of “conclusion,” it seems likely that these changes will cluster around three loci :

1) Those changes that are relatively quick-forming (like the finches)

2) Those changes that are relatively normal in their evolution ( like most species )

3) Those changes that take longer to obtain ( like alligators )

This process seems to be a normal thing. MOST changes will be clustered around that middle group, with a few evolutionary changes occurring around both extremes of relatively quick and relatively slow.

If all this is correct then why do so many who are firmly committed to evolution so strongly fight against pollution? It would seem to me they would welcome it so as to continue the natural selection. Usually evolutionists argue that human involvement via pollution is not good because evolution takes a long time and the pollution time frame is too short. However, this author is implying that the time frame is only long because there has not been much pollution till the present. interesting

I didn’t read the references but the author makes no mention of the underlying genetic changes. As she knows, evolution involves changes in the average genome of a species and the slight change in a physical trait does not necessarily indicate that.

This article talks about “natural” selection and the evolution of life that it causes. “Unnatural” selection, that caused by man, causes much greater effects on species over time, even without direct genetic tinkering.

I assume there are cases of man creating new species, i.e. a line of life that will not interbreed with its ancestor, partially satisfying Chris Calver’s observation above. Can anyone site any?

It is good though, that we have examples of evolution taking place without humans stepping in.

Stephen J. Gould’s Ontogeny and Phylogeny reopens a door that hints at Lamarckian answers to lightening fast heterochonic change. Changing the rates and timing of maturation speeds, if influenced by the environment, can result on evolution untraceable in the fossil record.

It’s possible the human evolution reveals this dynamic. Consider that autism is an evolutionary condition. The environment influences a mother’s testosterone level (proven to occur in many ways) raising it so high that when a child’s maturation rate is set at six weeks before birth, mother’s elevated testosterone might dramatically slow her son’s maturation rate. Autism is characterized by maturational delay.

Lightening fast evolution may characterize human evolution. Autism might be a response to new social conditions. Then the question becomes, if not randomly selected, why might maturational delay be selected?

The fact that evolution is a reality, does not in no manner exclude God from the scene, the reality is that evolution was started by God, but like good automatic machines of today all you have to do is start it the rest will be done without supervision, and also somethimes nature as well as your machine will go out of order, mainly because of us human who are also God’s creation

I am a well educated Episcopalian of Unitarian Bent. Docotoral Level Education. Last night I listened with great interest to the special on the Missoula Flood. As I listened and watched, I wondered what my Adventist Friends and Relatives would say or comment. It is clear to me that the Earth is a lot older than 7000 years. It is also clear to me that it is more likely that the Universe is 12 to 14 billion years old, and the Earth perhaps 4 – 5 billion years. I can accept we cam from a primordial stew. But it does puzzle me as to what started it all.

My wife was a Seventh Day Adventist, and I now live in a town with a major Seventh Day Adventist University. [It used to be college]

So, for years I have had to deal with this question on a very personal basis.

So I marvel at how otherwise sensible persons can claim there was intelligent design, or how they can refute the evidence of the Grand Canyon or the Missoula Flood.

When I see an article like the one above, I guess most of the “primitives” just have another reason to dislike the Times. They do, you know, generally.

Yes, everything involves. I haven’t been living in a cave but I was honestly shocked to find one can now get repair estimates online! I wonder if, like the decline in toad head sizes, change like this would result in a proportionate decline of dodgy mechanics as well. That’s another example of evolution right there though not quite in the context of this article.

It’s sad to think of how much the world around us changes while we barely pay attention.